1. Field of the Invention
The present invention relates to a liquid crystal display that can find wide application in various devices including notebook computers, mobile terminals, portable VTRs, and digital still cameras, and more particularly to a liquid crystal display having the functions of both reflective and transmissive types. That is, this liquid crystal display exhibits excellent visibility in both indoors and outdoors. Therefore, this liquid crystal display is suitable as a monitor display for a mobile terminal, a portable VTR, or a digital still camera.
Heretofore, semitransmissive LCDs (liquid crystal displays) having both reflecting function and transmitting function have been developed. Especially, a display device employing a vertically oriented liquid crystal of the semitransmissive type is described in JP-A-2002-350853 (patent reference 1).
FIGS. 6A and 6B show a related-art semitransmissive LCD. FIG. 6A is a schematic cross-sectional view of one pixel of this LCD. FIG. 6B is a schematic plan view of one pixel of the LCD. As shown in FIG. 6A, the LCD fundamentally includes a driving substrate 1, a counter substrate 2, and a liquid crystal material 3. A planarizing film 11 is formed on the inner surface of the driving substrate 1. Transparent pixel electrodes 12 and reflective electrodes 13 are formed on the planarizing film 11. A compensating plate 16, a λ/4 plate 14, and a polarization plate 15 are disposed on the outer surface of the driving substrate 1 that is made of glass or the like.
A color filter array 20 is formed on the inner surface of the counter substrate 2 and coated with a protective film 21. A transparent counter electrode 22 is formed on the protective film. A compensation plate 23, a λ/4 plate 24, and a polarization plate 25 are attached to the outer surface of the counter substrate 2 that is made of glass or the like.
The liquid crystal material 3 is oriented orthogonally to the driving substrate 1 and to the counter substrate 2. Therefore, the upper and lower interfaces in contact with the liquid crystal material 3 are oriented orthogonally in a manner not illustrated. Slits 31 are formed in the transparent pixel electrodes 12 on the side of the driving substrate 1. Protrusions 32 are formed on the surface of the counter electrode 22 on the side of the counter substrate 2. The slits 31 and protrusions 32 cooperate to split the orthogonally oriented liquid crystal material 3 in two dimensions.
As shown in FIG. 6B, each one pixel of the LCD is surrounded by signal lines 4 and gate lines 5. In this pixel, the portion where the transparent pixel electrode 12 is formed constitutes a transmissive region. Meanwhile, the portion where the reflective electrode 13 is formed constitutes a reflective region. As shown, the liquid crystal material 3 is split in two dimensions and oriented orthogonally by the slits 31 and protrusions 32. In the illustrated example, the liquid crystal material 3 in one transmissive region is split into two parts. Similarly, each one reflective region is split and oriented.
Referring again to FIG. 6A, the layer of the liquid crystal material 3 is made different in thickness between the reflective regions and the transmissive regions. For this purpose, a step 26 is added to the thickness of the protective film 21 formed on the side of the counter substrate 2. Because of the presence of the step 26, the thickness of the layer of the liquid crystal material 3 in the reflective regions is half of the thickness of the layer of the liquid crystal material 3 in the transmissive regions. Besides, pixel capacitors (not shown) arranged under the pixel electrodes 12 and pixel transistors (not shown) are formed on the driving substrate 1. The pixel transistors act to write signal voltages to the pixel electrodes 12 and to the pixel capacitors. The gates of the pixel transistors are connected with the gate lines 5. The sources are connected with the signal lines 4. The drains are connected with the pixel electrodes 12 and with the reflective electrodes 13.